Typical construction of digital image scanners, particularly those described as “flatbed scanners”, employs a generally rectangular-shaped scanner housing supporting a platen glass against which one may lay a piece of media, such as a piece of paper for scanning. An optical scanner head moves opposite the media and scanner associated software and/or firmware typically transforms an optical image of the media into a data file. Other scanners, often called “scroll feed scanners” function similar to a facsimile machine in that they feed sheets of paper through a stationary scanning mechanism one at a time.
Construction of flatbed scanners typically employs an optical carriage, housing an optical scanning head or the like; a carriage rod that aligns and guides the optical carriage down a scan-path below the platen; and a motorized drive mechanism employing a direct-current (DC) motor and/or stepper motor. The optical carriage has optics, also known as a scanner head, that normally employ mirrors. These optics map light at a location coinciding with the upper surface of the platen glass, where media is typically resting, to a charge couple device (CCD) or the like. The CCD converts optical photons into electrons, used to create a data signal. The data provided by the CCD is processed into a final form such as an image file, for example a bitmap (BMP) file, tag image file format (TIFF) file, Joint Photographics Expert Group (JPEG) file or the like.
In operation, the optics or scanner head of the carriage usually scans a very thin strip, commonly referred to as a scan line. Then typically the motorized drive mechanism translates the optical carriage one small step, and then the scanner head takes another scan line, followed by another step, and another scan. This step-and-scan process is repeated to create a rastered scan of a whole image of the media disposed against the platen.
Generally, drive technologies for scanner optical carriages attempt to translate a carriage in some controlled manner to create the scan lines for rastering together to create a digital image file. Multi-speed scanners use dynamic ranges of a drive motor to provide a multiple-speed carriage drive. Depending on the resolution required, some scanners may employ five or more speeds. Other motors may provide an infinite number of speeds, between an upper and a lower limit. In some scanners a pulse frequency to a stepper motor is modified to generate these different speeds. Another existing scanner carriage drive mechanism is a DC motor that employs a servo methodology.
A stepper motor has a rotor that moves through a fixed angle in response to a pulse from a controlling element. The stepper motor makes discrete steps that are translated to the carriage via a transmission and/or a belt and pulley system. The steps are based on characteristics of the stepper motor and/or a drive-train disposed between the stepper motor and scanner carriage. A stepper motor employs an open loop control system. A stepper motor driving a scanner carriage is sent a pulse and the system assumes the carriage moves one step in response. Therefore, existing stepper motor-based scanner carriage drives do not typically need intermediate position sensing.
A servo-drive mechanism typically employs a drive belt-and-pulley system to basically pull the carriage back and forth. Since this technology does not employ discrete steps, electronic logic to determine location, often based on velocity and/or acceleration of the carriage, is employed to provide a closed-loop control system. To this end, many DC servo scanner carriage drives include some type of optically-encoded position sensing, or the like. The DC servo, closed-loop system typically employs control algorithms. Otherwise, construction of these two types of existing scanner carriage drive systems are similar, employing a transmission and/or belt assembly.
Other types of scanner drive mechanisms may include screw drives, gear-wheel and rack drives, or the like. Screw drives may replace or augment the aforementioned carriage rod. A rack may be molded into, or attached to, the bottom of an existing scanner housing for a gear-wheel and rack-drive mechanism. Regardless, drive technologies for scanner carriages are intended to translate a scanner carriage in a controlled manner to facilitate creation of scan lines to be rastered together to develop a digital image.
Increasing resolution capability demanded by the scanner market translates into smaller and smaller steps between scan lines to provide higher resolutions, that in turn, results in slower scan speeds. However, extremely fast scans at low-resolution, such as used for a preview scan, are in demand as well. Existing scanner carriage drive motors specifically designed for high-resolution, high-accuracy scans typically do not have very fast performance at lower resolutions. DC servo or stepper motors only have a limited dynamic range, limiting the upper speed threshold that a scanner carriage may be moved so as to provide the required precise high-resolution, slow-speed scans. For example, stepper motors can only pulse within a limited range of frequencies. Problematically, use of a dual-speed transmission or two different motors with different drive speeds is not desirable as it raises cost and complexity issues.
Uses for springs in the scanner or copier industry abound. For example, springs of various types are used to provide vibration or oscillation for universal product code (UPC) scanners or the like as disclosed in Goto, U.S. Pat. No. 5,245,463; Giordano, U.S. Pat. No. 5,594,232; and Dvorkis, U.S. Pat. Nos. 5,621,371 and 5,412,198. A spring may be employed in conjunction with a motor-driven cable to tension a carriage drive cable and/or to stabilize a scan head by dampening vibration in such a cable. U.S. Patents related to such use of a spring in a scanner or copier include: Yoshida, U.S. Pat. No. 5,392,100; Takizawa, U.S. Pat. No. 4,171,901; Hediger, U.S. Pat. No. 4,965,638; Satomi, U.S. Pat. No. 4,771,315; Hayashi, U.S. Pat. No. 6,108,505; Peng, U.S. Pat. No. 6,026,261; and Costanza, U.S. Pat. No. 4,218,127. Forrester, U.S. Pat. No. 4,460,268, and Cook, U.S. Pat. No. 3,918,806 are examples of copier mechanisms driven by dash pots that use a spring to rapidly return the copier head to a start position, without copying during the return.